In the development trend of electronic industry, electronic products get thinner and lighter with high performance, function and speed. In addition, it is a trend to enhance beat dissipation to meet requirement of electronic devices with long life.
A conventional package substrate for attaching a light emitting diode (LED) 14 is shown in FIG. 1A and FIG. 1B. A ceramic substrate 10 having a surface 10a and a surface 10b, a bonding layer 13 is formed on the surfaces 10a and 10b of the ceramic substrate 10, and conductive holes 100 are formed through the ceramic substrate 10 for electrically connecting the bonding layer 13 on the surfaces 10a and 10b of the ceramic substrate 10. A light emitting diode 14 is mounted on the bonding layer 13 on the surface 10a of the ceramic substrate 10.
As shown in FIG. 1A, the P electrode and the N electrode of the LED 14 are disposed on the same surface of the LED 14, such that the P electrode and the N electrode of the LED 14 are connected to the bonding layer 13 via wirings 15. Alternatively, as shown in FIG. 1B, the P electrode and the N electrode of the LED 14′ are disposed on different surfaces of the LED 14′, and thus one electrode is connected to the bonding layer 13 via a wiring 15, and the other electrode is directly and electrically connected to the bonding layer 13.
Heat generates during the operation of the LED 14, 14′, and the heat is introduced to the surface 10b of the ceramic substrate 10 is conductive holes 100. In addition the material of the ceramic substrate 10 also facilitates heat dissipation.
However, the conventional ceramic substrate 10 has the coefficient of thermal conductivity as 17-170 w/m·k, which is significantly smaller than that (250 w/m·k) of aluminum material and also smaller than that (400 w/m·k) of copper material. The ceramic substrate 10 has worse thermal conductivity and heat dissipation than metal material. The bonding layer 13 and the conductive holes 100 facilitate heat dissipation, but the volume of the conductive holes 100 is much smaller than that of the ceramic substrate 10. Therefore, the heat dissipation efficiency of the ceramic substrate 10 is not compatible with metal materials.
Accordingly, there is an urgent need to enhance the effect of heat dissipation in the art.